The goal of this research is to continue the investigation of motor coordination of song production in songbirds. The main focus will be on aspects of song production and modification that have received little or no attention to date. The various peripheral motor patterns will be studied in spontaneously singing birds with a set of well-established techniques, including recording of airflow and respiratory pressure, electrical activity of muscles and beak movements. To investigate the integration of beak movements into the motor control of song production, beak movements will be recorded during song development and again after song has become stereotyped. In addition, the role of the jaw muscles effecting these movements will be investigated for the first time. The dependence of beak movements on acoustic feedback will be studied by manipulating song output. The investigation into the detailed role of the muscle systems controlling the two independent sound generators will be continued by completing electromyographic recordings in two species. In addition to elucidating the role of syringeal muscles in the generation of various sounds, this research will allow the first assessment of whether different individuals can generate similar sounds using different combinations of muscle activation patterns or whether constraints dictate a certain pattern. Finally, the physiological and histological characteristics of the various muscles involved in sound generation and modification will be investigated for the first time. This information will be very important in assessing the peripheral constraints on temporal and acoustic modulation of song. Knowing the limits of the peripheral systems will then allow inferences about necessary features, such as temporal precision and coordination, of the central motor control systems. An additional level of complexity in motor coordination will be explored in the brown-headed cowbird by studying the development of the intricate integration between the complex visual display and song. Together these experiments will advance our knowledge of peripheral motor events that lead to the production of song in songbirds. Because singing is a complex, learned vocal behavior with many parallels to human speech and singing, the results of the proposed experiments will not only further our basic knowledge about motor control but also enhance our understanding of similarities and differences between this animal model system and the human system.